Attenuator having phase between input and output signals independent of attenuation

ABSTRACT

An attenuator includes first resistors that are connected in series to each other at connection nodes and between an input node and a fixed voltage node, voltage output nodes coupled to the input node and the respective connection nodes of the first resistors, switches and corresponding second resistors being respectively connected in series between the connection nodes and voltage output nodes and commonly connected to an output node, and a load capacitance connected between an output node and the fixed voltage node. The phase between input and output signals is independent of the attenuation. A phase difference is added by the second resistor so that the phase shift determined by the voltage dividing ratio of the first resistors selected by closing a switch and by the value of the load capacitance is compensated.

FIELD OF THE INVENTION

The present invention relates to an attenuator and, more particularly, to a voltage dividing type attenuator attenuating a reference voltage signal with a reference step.

BACKGROUND OF THE INVENTION

FIGS. 3(a) and 3(b) show a circuit construction of a prior art attenuator and its input and output waveforms. FIG. 3(a) is circuit diagram of the attenuator, and FIG. 3(b) is a diagram illustrating the output waveforms against its input signal. In FIG. 3(a), a signal applied to an input terminal V_(IN) is divided by a dividing circuit of resistors R₀₁, R₁₂, R₂₃, R₃₄, R₄₅ and R_(5G) which are serially connected to each other between the input terminal V_(IN) and the ground. This divided signal is obtained from an output terminal V_(OUT) by turning on one of the switches of a switch SW₀ connected between the input terminal V_(IN) and the output terminal V_(OUT), a switch SW₁ connected between the resistors R₀₁ and R₁₂ at its one end and connected to the output terminal V_(OUT) at the other end, a switch SW₂ connected between the resistors R₁₂ and R₂₃ at its one end and connected to the output terminal V_(OUT) at the other end, a switch SW₃ connected between the resistors R₂₃ and R₃₄ at its one end and connected to the output terminal V_(OUT) at the other end, a switch SW₄ connected between the resistors R₃₄ and R₄₅ at its one end and connected to the output terminal V_(OUT) at the other end, and a switch SW₅ connected between the resistors R₄₅ and R_(5G) at its one end and connected to the output terminal V_(OUT) at the other end. Reference character C designates a load capacitance between the output terminal V_(OUT) and the ground potential.

A description is given of the operation.

Suppose that a signal V_(i) input to the input terminal V_(IN) is a sinusoidal wave of angular frequency ω and wave height, i.e., amplitude, V₀. This signal V_(i) is divided by the serially connected resistors R₀₁, R₁₂, R₂₃, R₃₄, R₄₅ and R_(5G), and for example, the divided voltage V₁ appearing at a node between the resistors R₁₂ and R₂₃ of a wave height V₁ is represented by the following formula (1): ##EQU1## Thereupon, when only the switch SW₂ is turned on, an output signal V_(o) of wave height V₁ shown in the formula (1) is output to the output terminal V_(OUT).

Similarly, the divided voltage V₂ appearing at a node between the resistors R₄₅ and R_(5G) of a wave height V₂ is represented by the following formula (2): ##EQU2## Thereupon, when only the switch SW₅ is turned on in place of the switch SW₂, the output signal V₀ of the wave height V₂ as shown in the formula (2) is output to the output terminal V_(OUT) with its angular frequency ω₀.

When the wave height of the input signal is V₀, the angular frequency thereof is ω, and the phase delay thereof is ω·t₀, the input signal V_(i) is represented by the following formula (3):

    V.sub.i =V.sub.0 ·sin ω(t-t.sub.0)          (3)

And when the wave height of the output signal is V_(m), the angular frequency thereof is ω, and the phase delay thereof is ω·t_(d), the input signal V_(o) is represented by the following formula (4):

    V.sub.0 =V.sub.m ·sin ω(t-t.sub.d)          (4)

FIG. 3(b) shows waveforms of the input signal V_(i) and the output signal V_(o). In the output waveform, when only the switch SW₂ is turned on, the wave height V_(m) becomes V₁ given by the formula (1), and the delay time t_(d) becomes (t₀ +t₁), and the formula (4) becomes the following formula (5):

    V.sub.0 (SW.sub.2)=V.sub.1 ·sin ω(t-t.sub.0 -t.sub.1)(5)

In addition, when only the switch SW₅ is turned on, the wave height V_(m) becomes V₂ as given by the formula (2), and the delay time t_(d) becomes (t₀ +t₂), and the formula (5) becomes the following formula (6):

    V.sub.0 (SW.sub.5)=V.sub.2 ·sin ω(t-t.sub.0 -t.sub.2)(6)

The prior art attenuator is constructed as described above, and there arises a deviation in phase dependent on the degree of attenuation, and also it was difficult to control the phase of the output signal so as to compensate the deviation in phase.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an attenuator keeping the phase difference between the input signal and the output signal constant independent of the attenuated quantity.

Other objects and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific embodiment are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.

According to a first aspect of the present invention, an attenuator includes a plurality of first resistors that are connected in series to each other between an input node to which an input signal to be attenuated is applied and a predetermined voltage node. A plurality of voltage output nodes are connected to the input node and the connection nodes of adjacent first resistors. A plurality of switches, only one of which is selectively closed at a time, are respectively connected to the plurality of voltage output nodes, one end of each of a plurality of second resistors is connected to an output terminal of a corresponding switch of the plurality of switches and the other ends of the second resistors are commonly connected to provide an output node for outputting an attenuated output signal. A load capacitance is connected between the output node and the predetermined voltage node. By this construction, the phase difference that arises in accordance with the attenuation quantity, a phase amount that is determined dependent on the phase difference is added by the second resistor. The resistance of the second resistor is determined so that the phase shift amount of the output signal against the input signal, determined by the voltage dividing ratio of the first resistors and the capacitance value of the load capacitance, does not depend on the attenuation quantity, that is, in accordance with the selected switch, whereby even when any attenuation quantity is selected, an attenuated output of a constant phase difference can be easily obtained without deteriorating the precision of the voltage division for the attenuation.

According to a second aspect of the present invention, an attenuator includes a plurality of first resistors that are connected in series to each other between an input node to which an input signal to be attenuated is input and a predetermined voltage node. A plurality of voltage output nodes are connected to the input node and respective ones of a plurality of connection nodes between adjacent first resistors, one end of each of a plurality of second resistors is connected a corresponding one of the plurality of voltage output nodes, respectively, the plurality of output nodes outputting attenuated output signals to the other ends of the plurality of second resistors, respectively. A plurality of load capacitances are connected between the plurality of output nodes and the predetermined voltage node, respectively. By this construction, to the phase difference that arises in accordance with the attenuation, a required phase amount that is dependent on the phase difference is added by the second resistor. The resistance of the second resistor is determined so that the phase shift of the output signal against the input signal, is determined by the voltage dividing ratio of the first resistors and the capacitance value of the load capacitance, and does not depend on the attenuation quantity, i.e., on the output node, whereby a plurality of attenuated outputs having a constant phase difference can be obtained at the same time easily and without deteriorating the precision of the voltage division for the attenuation.

According to a third aspect of the present invention, in an attenuator, the resistance values of the second resistors are selectable using the plurality of resistors and switches and, therefore, the phase difference between the input and the output can be can finely adjusted by positively varying the phase difference between the input and the output to some degree.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a circuit diagram illustrating an attenuator according to a first embodiment of the present invention, and FIG. 1(b) is a diagram showing the input and output waveforms thereof.

FIG. 2(a) is a circuit diagram illustrating an attenuator having multiple outputs according to a second embodiment of the present invention, and FIG. 2(b) is a diagram showing the input and output waveforms thereof.

FIG. 3(a) is a circuit diagram illustrating an attenuator according to a prior art, and FIG. 3(b) is a diagram showing the input and output waveforms thereof.

FIG. 4 is a diagram illustrating an attenuator according to a third embodiment of the present invention in which the phase difference can be varied.

FIG. 5 is a diagram illustrating an attenuator according to a fourth embodiment of the present invention which is an alternative of the third embodiment of FIG. 4.

FIG. 6 is a diagram illustrating an equivalent circuit that is employed when the formula (7) is applied

FIG. 7 is a diagram illustrating a vector diagram that is employed when the formula (7) is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1.

FIG. 1(a) is a circuit diagram illustrating an attenuator according to a first embodiment of the present invention, and FIG. 1(b) shows the input and output waveforms.

In FIG. 1(a), a signal applied to an input terminal V_(IN) is divided by six resistors R₀₁, R₁₂, R₂₃, R₃₄, R₄₅, and R_(5G) connected in series to each other between the input terminal V_(IN) and the ground. One end of the switch SW_(o) is connected to the input terminal V_(IN) and one end of the switches SW₁, SW₂, SW₃, SW₄, and SW₅ is respectively connected to a connection node of two adjacent resistors, and the other ends of the six switches are commonly connected to one output terminal V_(OUT), respectively through resistors R₀, R₁, R₂, R₃, R₄, and R₅. It is supposed that these six resistors R_(O), R₁, R₂, R₃, R₄, and R₅ produce respective phase differences of θ₀, θ₁, θ₂, θ₃, θ₄, and θ₅ in the divided input signal at the respective connection nodes of the resistors R₀₁, R₁₂, R₂₃, R₃₄, R₄₅, and R_(5G) and the six switches SW₀, SW.sub.,1, SW₂, SW₃, SW₄, and SW₅, respectively.

Then, suppose that the phase difference between the output and the input is θ_(out), if the resistance values of the respective resistors R_(n) (n=1-5) are set so that a phase shift that is determined by the phase difference may be applied to the phase difference that arises dependent on the attenuation quantity so as to produce a constant phase difference when any switch is selected, the phase difference between the input and output becomes constant even when any switch is thus selected. In order to realize this, the resistance values to be possessed by the respective resistors R_(n) (n=1-5) are given by the following formula (7), ##EQU3## value is ascertained by inputting a signal similar to the signal that is to be input. In the formula (7), reference character C represents a load capacitance of the output signal.

Therefore, when only the switch SW₀ is closed, an output wave V₀ of wave height V_(A), and phase delay ω(t₀ +t₃) is obtained. In addition, when only the switch SW₂ is closed, an output of wave height V_(B) and phase delay ω(t₀ +t₃) is obtained, and when only the switch SW₅ is closed, an output of wave height V_(C) and phase delay ω(t₀ +t₃) is obtained. These outputs are represented by the following formula (8), (9), (10):

    V.sub.0 (SW.sub.0)=V.sub.A ·sin ω(t-t.sub.0 -t.sub.3)(8)

    V.sub.0 (SW.sub.2)=V.sub.B ·sin ω(t-t.sub.0 -t.sub.3)(9)

    V.sub.0 (SW.sub.5)=V.sub.C ·sin ω(t-t.sub.0 -t.sub.3)(10)

Here,

    V.sub.A =V.sub.0                                           (11)

    V.sub.B =V.sub.1                                           (12)

    V.sub.C =V.sub.2                                           (13)

    θt.sub.3 =θ.sub.out                            (14)

In this first embodiment, because the resistance values of the respective resistors connected in series to the plurality of switches are chosen based upon the phase difference added to the phase difference that arises dependent on the attenuation quantity, even when any switch is closed, the phase difference between the signal that is obtained from the output terminal and the signal that is input to the input terminal is constant. Even when any output signal having any attenuation quantity is selected, the phase difference between the input and the output signals can be made constant, regardless of the attenuation quantity.

The above-described formula (7) can be derived as described above.

The output signal V_(o), when a resistor R is serially inserted to the input signal V_(i) at an angular frequency ω and with a phase delay θ_(i), is represented by the following formula: ##EQU4## Therefore,

    V.sub.0 /V.sub.i =(1-jωCR)/{1+(ωCR).sup.2 }    (15)

Therefore, the phase delay θ₀ of the signal V_(o) v becomes: ##EQU5##

Therefore, the phase difference (θ₀ -θ_(i)) becomes,

    θ.sub.0 -θ.sub.i =-tan.sup.-1 ωCR        (16)

This is represented by vector representation as shown in FIG. 7.

Therefore, the general formula of v_(i), v_(o) become as in the following formula:

    V.sub.i =V.sub.0 ·sin (ωt-θ.sub.i)    (17)

    V.sub.0 =V.sub.m ·sin (ωt-θ.sub.0)    (18)

When the phase difference of formula (16) is made as θ₁, the formula (18) becomes:

    V.sub.0 =V.sub.m ·sin (ωt-θ.sub.0 -θ.sub.1)(19)

From the above, by the circuit of FIG. 6 in which one resistor R is inserted in series to the input signal v_(i), the output signal can be delayed with relative to the input signal by an amount of θ₁ (=θ₀ -θ_(i)) represented by the formula (16).

In other words, the value of the resistance R that can delay the output signal relative to the input signal by θ1 in FIG. 6 is obtained from the formula (16), as: ##EQU6##

The above-described formula (7) can be derived in this way. In addition, the formulae (8), (9), and (10) can be obtained respectively by making the phase delay that of ω(t₀ -t₃) by inserting a resistor having a value obtained from the formula (7).

While in this first embodiment there are six switches SW₀, SW₁, SW₂, SW₃, SW₄, and SW₅ and resistors R₁, R₂, R₃, R₄, and R₅ there may be any number equal to the number of the resistors connected between the input terminal and ground, and the same effects are also obtained as in the first embodiment.

Embodiment 2.

While in the first embodiment an attenuation output having a constant phase difference is obtained by employing a plurality of switches, it is also possible to provide a construction in which various attenuated outputs are output with a constant phase difference between the input signal and the output signal, by removing these switches from the first embodiment.

FIG. 2(a) shows a circuit diagram of an attenuator according to a second embodiment of the present invention that has such a construction, and FIG. 2(b) shows three output waveforms among six outputs together with the input waveform.

In FIG. 2(a), the signal input to the input terminal V_(IN) is divided by the six resistors R₀₁, R₁₂, R₂₃, R₃₄, R₄₅, and R_(5G) which are connected in series between the input terminal V_(IN) and the ground. Then, the divided signal is respectively output to six output terminals V_(out0), V_(out1), V_(out2), V_(out3), V_(out4), and V_(out5), respectively, via six resistors R₀, R₁, R₂, R₃, R₄, and R₅, respectively. One end of resistor R_(o) is connected to the input terminal V_(IN) and the resistors R₁, R₂, R₃, R₄, and R₅ are respectively connected to the five connection nodes of the adjacent resistors R₀₁, R₁₂, R₂₃, R₃₄, R₄₅, and R_(5G).

Here, the resistance values of the resistors R_(n) (n=1-5) are given by the formula (7) similarly as in the first embodiment.

Therefore, from the terminal V_(out0), an output waveform V_(o) of wave height V_(A) and phase delay ω(t₀ +t₃) is obtained. In addition, an output of wave height V_(B) and phase delay ω(t₀ +t₃) and an output of wave height V_(C) and phase delay ω(t₀ +t₃) are obtained from the output terminal V_(out3) and from the output terminal V_(out5) respectively at the same time. These are given by the formulae (8), (9), and (10), respectively.

In this way, according to this second embodiment, because the resistance values of the resistors provided between the connection nodes of the voltage dividing resistors and the output terminals are set to values that add a required phase value dependent on the phase difference that depends on the attenuation quantity, the signals that are obtained from any output terminal have a constant phase difference relative to the signal input to the input terminal V_(IN), and it is possible to make the phase difference between the input and the output signal constant regardless of the attenuation quantity.

While in this second embodiment, six switches SW₀, SW₁, SW₂, SW₃, SW₄, and SW₅ and six resistors R₁, R₂, R₃, R₄, and R₅ are provided, these elements may be provided in any number equal to the number of the resistors connected between the input terminal and ground and the same effects are also obtained as in the second embodiment.

Embodiment 3.

While in the above-described first and second embodiments, the attenuators produce a constant phase difference between the input and the output independent of the attenuation quantity, it is also possible to construct an attenuator so that the phase difference is actively varied to some degree so as to finely adjust the phase difference.

FIG. 4 illustrates a circuit diagram of an attenuator according to a third embodiment of the present invention having such a construction. In FIG. 4, an element corresponding to the resistor R_(n) in FIG. 1(a) which is connected in series to the n-th switch SW_(n), includes five resistors R_(n1), R_(n2), R_(n3), R_(n4), R_(n5), one end of each of which is connected to the output end of the switch SW_(n) via respective switches SW_(n1), SW_(n2), SW_(n3), SW_(n4), SW_(n5). The other ends of the resistors R_(n1), R_(n2), R_(n3), R_(n4), R_(n5) are commonly connected to provide a connection node, which is connected to the output terminal of the attenuator, so as to enable to vary the resistance value.

In this attenuator of the third embodiment, because it is possible to select among the five resistance values R_(n1), R_(n2), R_(n3), R_(n4), R_(n5) as the resistance value of the resistor R_(n) by closing only one among the five switches SW_(n1), SW_(n2), SW_(n3), SW_(n4), SW_(n5), the resistance value R_(n) can be finely adjusted, and the phase difference can be positively varied to some degree.

While in this third embodiment, six switches SW₀, SW₁, SW₂, SW₃, SW₄, and SW₅ and six resistors R₁, R₂, R₃, R₄, and R₅ are provided, these elements may be provided in any number equal to the number of resistors corrected in series between the input terminal and ground, and the same effects are also obtained as in the third embodiment.

Embodiment 4.

While in the above-described third embodiment, only one resistor is selected among the five resistors as a resistor giving a phase difference, this resistor that gives a phase difference may be variable, dependent on how many resistors are connected in series to each other.

FIG. 5 illustrates an attenuator according to a fourth embodiment having such a construction.

In this FIG. 5, an element corresponding to the resistor R_(n) in FIG. 1 which is connected in series to the n-th switch SW_(n), includes five resistors R_(n1), R_(n2), R_(n) 3, R_(n4), R_(n5) which are connected in series to each other. One terminal of the resistor R_(n1) is connected to the other end of the switch SW_(n). Five switches SW₁, SW_(n2), SW_(n3), SW_(n4), SW_(n5) are respectively connected to the four connection nodes of adjacent serially connected resistors. Switch SW_(n5) is connected to the resistor R_(n5), respectively, and the other ends of the switches SW_(n1), SW_(n2), SW_(n3), SW_(n4), SW_(n5) are commonly connected to each other to provide one connection node, which is connected to the output terminal of the attenuator.

In this fourth embodiment, it is possible to select a resistance value of the resistor R_(n) among five resistance values of R_(n1), R_(n1) +R_(n2), R_(n1) +R_(n2) +R_(n3), R_(n1) +R_(n2) +R_(n3) +R_(n4), R_(n1) +R_(n2) +R_(n3) +R_(n4) +R_(n5), and thus, the resistance value R_(N) can be finely adjusted and therefore the phase difference can be positively finely adjusted to some degree.

While in this fourth embodiment, six switches SW₀, SW₁, SW₂, SW₃, SW₄, and SW₅ and five resistors R₁, R₂, R₃, R₄, and R₅ are provided, respectively, these elements may be provided in any number equal to the number of the resistors connected in series between the input terminal and ground and the same effects are also obtained as in the fourth embodiment.

According to a first aspect of the present invention, a plurality of first resistors are connected in series to each other between an input node to which an input signal to be attenuated is applied and a predetermined voltage node, a plurality of voltage output nodes are provided, one connected to the input node and others to the connection nodes of the adjacent resistors, respectively. Input nodes of a plurality of switches, only one of which is selectively closed, are respectively connected to the plurality of voltage output nodes, a plurality of second resistors are connected to the output terminals of the plurality of switches, and the other ends of the second resistors are commonly connected to provide an output node for outputting an attenuated output signal, and a load capacitance is connected between the output node and the predetermined voltage node. By this construction, to the phase difference that arises in accordance with the attenuation quantity, a phase amount that is determined dependent on the phase difference is added by the second resistor, the resistance of which is determined so that the phase shift amount of the output signal against the input signal is determined by the voltage dividing ratio of the first resistors and the capacitance value of the load capacitance, and does not depend on the attenuation quantity selected by the switch, whereby even when any output signal of having any attenuation quantity is selected, an attenuated output of a constant phase difference can be easily obtained without deteriorating the precision of the voltage division in the attenuation.

According to a second aspect of the present invention, a plurality of first resistors are connected in series to each other between an input node to which an input signal to be attenuated is input and a predetermined voltage node, one of a plurality of voltage output nodes is connected to the input node and the other output nodes are connected to connection nodes between adjacent first resistors, one end of each of the second resistors is connected to one of the plurality of voltage output nodes, respectively, the plurality of output nodes outputting attenuated output signals to the other ends of the plurality of second resistors, respectively, and a plurality of load capacitances are connected between the plurality of output nodes and the predetermined voltage node, respectively. By this construction, to the phase difference that arises in accordance with the attenuation quantity, a required phase amount that is dependent on the phase difference is added by the second resistor, the resistance of which is determined so that the phase shift amount of the output signal against the input signal, that is determined by the voltage dividing ratio of the first resistors and the capacitance value of the load capacitance, and does not depend on the attenuation quantity, whereby a plurality of attenuated outputs having a constant phase difference can be obtained at the same time easily without deteriorating the precision of the voltage division in the attenuation.

According to a third aspect of the present invention, the resistance values of the second resistors are made variable by a plurality of resistors and switches and therefore, the phase difference between the input and the output can be can finely adjusted by positively varying the phase difference between the input and the output to some degree. 

What is claimed is:
 1. An attenuator comprising:an input node to which an input signal to be attenuated is input; a plurality of first resistors connected at connection nodes in series between said input node as a first of said connection nodes and a second node; a plurality of voltage output nodes including a first voltage output node coupled to said input node and other voltage output nodes respectively coupled to respective connection nodes of said plurality of first resistors; a plurality of switches, each switch being coupled to a respective voltage output node and a respective connection node; a plurality of second resistors, each second resistor being connected in series to one of said switches between a connection node and an output node from which an attenuated output signal is taken, one end of each of said plurality of series connections of said switches and second resistors being commonly connected at an output node; and a load capacitance connected between said output node and said second node wherein said respective second resistors have resistances determined so that an output signal at said output node has a phase relative to an input signal that is determined by a dividing ratio of said first resistors and said load capacitance independent of signal attenuation selected by closing one of said switches.
 2. The attenuator of claim 1 wherein at least one of said second resistors includes a plurality of auxiliary resistors and corresponding auxiliary switches serially connected to respective auxiliary resistors, said serial connections of said auxiliary resistors and switches being connected in parallel for varying the resistance of said at least one second resistor by closing one of said auxiliary switches.
 3. The attenuator of claim 1 wherein at least one of said second resistors comprises n auxiliary resistors connected in series to each other at connection nodes and n auxiliary switches, each auxiliary switch having first and second terminals, said first terminals being commonly connected and said second terminals being connected to respective common connection nodes of said auxiliary resistors for varying the resistance of said at least one second resistor by closing one of said auxiliary switches.
 4. An attenuator comprising:an input node to which an input signal to be attenuated is input; a plurality of first resistors connected at connection nodes in series between said input node as a first of said connection nodes and a second node; a plurality of voltage output nodes including a first voltage output node coupled to said input node and other voltage output nodes respectively coupled to respective connection nodes of said plurality of first resistors; a plurality of second resistors, each second resistor being respectively connected to a corresponding one of said connection nodes and voltage output nodes; and a plurality of load capacitances respectively connected between a corresponding output node and said second node wherein said respective second resistors have resistances determined so that an output signal at an output node has a phase relative to an input signal that is determined by a dividing ratio of said first resistors and said load capacitances is independent of signal attenuation at a selected output node.
 5. The attenuator of claim 4 wherein at least one of said second resistors includes a plurality of auxiliary resistors and corresponding auxiliary switches serially connected to respective auxiliary resistors, said serial connections of said auxiliary resistors and switches being connected in parallel for varying the resistance of said at least one second resistor by closing one of said auxiliary switches.
 6. The attenuator of claim 4 wherein at least one of said second resistors comprises n auxiliary resistors connected in series to each other at connection nodes and n auxiliary switches, each auxiliary switch having first and second terminals, said first terminals being commonly connected and said second terminals being connected to respective common connection nodes of said auxiliary resistors for varying the resistance of said at least one second resistor by closing one of said auxiliary switches. 